Dry photoconductographic process



United States Patent 3,232,852 DRY PHOTOCONDUCTOGRAPHEC PROCESS Franz Urbach and Nelson R. Nail, Rochester, N.Y., as-

signors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Oct. 25, 1960, Ser. No. 64,902 8 Claims. (Cl. 204-18) This invention relates to photoconductography.

Photoconductography forms a complete image at one time or at least a non-uniform part of an image as distinguished from facsimile which at any one time produces only a uniform dot. The present invention relates particularly to a dry or at least substantially dry system of photoconductography.

Cross reference is made to the following series of applications filed July 28, 1960:

Serial No. 45,940, John W. Castle, Jr., Photoconductography Employing Reducing Agents.

Serial No. 45,941, Raymond F. Reithel, Photoconductolithography Employing Nickel Salts, now abandoned, now continuation-impart Serial No. 120,863, filed June 7, 1961, now US. Patent 3,106,157.

Serial No. 45,942, Raymond F. Reithel, Photoconductolithography Employing Magnesium Salts, now U.S. Patent 3,033,179.

Serial No. 45,943, Raymond F. Reithel, Photoconductography Employing Spongy Hydroxide Images, now abandoned, now continuationdn-part Serial No. 120,035, filed June 27, 1961, now US. Patent 3,106,518.

Serial No. 45,944, Raymond F. Reithel, Method for Making Transfer Prints Using a Thotoconductographic Process.

Serial No. 45,945, Raymond F. Reithel, Photoconductography Employing Manganese Compounds, now abandoned.

Serial No. 45,946, Raymond F. Reithel, Photoconductography Employing Molybdenum or Ferrous Oxide, now abandoned, now continuation-in-part Serial No. 120,036, filed June 27, 1961, now US. Patent No. 3,106,156.

Serial No. 45,947, Raymond F. Reithel, Photoconductography Employing Cobaltous or Nickelous Hydroxide, now abandoned, now continuation-in-part Serial No. 120,037, filed June 27, 1961, now US. Patent 3,057,788.

Serial No. 45,948, Donald R. Eastman, Electrophotolithography.

Serial No. 45,949, Donal-d R. Eastman, Photoconductolithography Employing Hydrophobic Images, now US. Patent 3,152,969.

Serial No. 45,950, Donald R. Eastman and Raymond F. Reithel, Photoconductography Employing Electrolytic Images To Harden or Soften Films, now US. Patent 3,106,516.

Serial No. 45,951, Donald R. Eastman and Raymond F. Reithel, Photoconductography Employing Absorbed Metal Ions, now abandoned, and now continuation-inpart Serial No. 120,038, filed June 27, 1961.

Serial No. 45,952, Donald R. Eastman and Raymond F. Reithel, Photoconductography Employing Spongy Images Containing Gelatin Hardeners, now US. Patent 3,106,517.

Serial No. 45,953, John J. Sagura, Photoconductography Employing Alkaline Dye Formation, now US. Patent 3,057,787.

Serial No. 45,954, John J. Sagura and James A. Van Allan, Photoconductography Employing Quaternary Salts, now US. Patent 3,178,362.

Serial No. 45,955, Franz Urbach and Nelson R. Nail, Uniform Photoconductographic Recording on Flexible Sheets, now abandoned.

Serial No. 45,956, Franz Urbach and Nelson R. Nail,

3,232,852 Patented Feb. 1, 1966 ice High Contrast Photoconductographic Recording, now abandoned.

Serial No. 45,957, Nicholas L. Weeks, Photoconductography Involving Transfer of Gelatin.

Serial No. 45,958, Donald R. Eastman, Photoconductolithography Employing Rubeanates, now US. Patent 3,095,808.

Serial No. 45,959, Donald R. Eastman and Raymond F. Reithel, Electrolytic Recording With Organic Polymers. now US. Patent 3,106,155.

Serial No. 46,034, Franz Urbach and Donald Pearlman, Electrolytic Recording, now abandoned.

Cross reference is also made to cofiled applications Serial No. 64,901 and 64,903 both to Franz Urbach.

Electrolytic facsimile systems are well known. Electrolytic photoconductography is also known and is described in detail in British 188,030, Von Bronk and British 464,112, Goldmann, modifications being described in British 789,309, Berchtold and Belgium 561,403, Johnson et al.

It is possible in photoconductographic processes according to the present invention to employ an extremely thin electrolytic layer or to use solid electrolytes such as the silver halides including silver chloride, silver bromide, silver iodide and the complex silver halides such as silver mercuric iodide. The photoconductor may be selenium but the commonest commercial form is photoconductive zinc oxide in resin coated on a metal foil, paper, laminate. The zinc oxide photoconductor has the advantage that the conductivity image created therein by exposure persists and may be developed subsequent to, rather than during, the exposure. However, the present invention works equally well with the photoconductographic systerns employing post exposure development and those employing development during exposure. On the other hand if a silver halide crystal layer is pressed into contact with a zinc oxide (in resin) layer containing a conductivity image, the image quality is inferior in density and resolution and the image appears primarily on the silver halide which is objectionable rather than on the Zinc oxide.

According to a preferred form of the present invention intimate electric contact between the dry electrolyte and the photoconductor is provided by an electrically conducting material less than 0.0003 cm. thick and having an optical density in transmission of less than 0.3

pressed between the halide and the photoconductor. In one species this contacting layer is a metal such as silver or aluminum evaporated or chemically coated on the zinc oxide layer itself prior to exposure. The metal layer must not have sufiicient thickness to have serious lateral conductivity, and further the optical density produced on the ZnO layer must not be so high that the further adidtion of optical density by deposition of image material gives poor image contrast. These conditions are met in general by using metal layers thinner than about angstroms or, as another description of the same thing, by using metal layers which when deposited on glass show a transmission density in the visible region of less than 0.3. The metal layer is so thin as to be practically invisible but is still adequate to provide good electrical contact between the crystalline silver bromide, for example, and the photoconductor. The image forms on the metallic material and zinc oxide.

In another species, a single drop of water is spread completely over the zinc oxide layer and the sandwich is subjected to sufiicient pressure to reduce the thickness of the water to less than the 0.0003 cm. limit mentioned. Since the image forms at the interface between the water and the zinc oxide lateral conductivity is not objectionable. Thus thicker layers of water are: still operative,

but are undesirable because they leave the finished print sensibly wet after separation of the print from the silver halide layer.

The water can be distilled water or can contain salts to increase the conductivity. The distilled water appears to work equally well, however, and therefore there appears to be no need to add other materials. Again the image quality is excellent and the image deposits on the zinc oxide layer. The total quantity of water present is so small that the zinc oxide layer is sensibly dry at all times and particularly as it is removed from the silver halide solid electrolyte. Thus both of these species use a solid dry electrolyte but add metal or water solely to insure intimate electric contact with the photoconductor.

Another species of the invention employs an electrolyte which is not quite as rigid as silver halide crystals but is still a solid. The electrolyte is gelatin containing ions which are either heavy metal ions or which during the passage of current are replaced by heavy metal ions from a heavy metal anode. not have sufi icient conductivity to act as an electrolyte, therefore a very minute percentage of Water molecules must be present. According to this species of the invention, these molecules of Water are provided by incorporating in the gelatin a small percentage of a humectant such as glycerol. The amount is sufficient to make the gelatin electrically conducting (i.e. to lower its electrical resistance several orders of magnitude) but not sufficient to make the gelatin tacky or moist to the touch even when in contact with atmospheric humidity as high as 85% relative humidity. The function of the glycerol, not fully understood, may alternatively be to provide sufiicient flexibility in the gelatin layer to allow its surface to make intimate electrical contact with the metallic anode; there probably is sufiicient water in the plain gelatin but it is too stiff to make the necessary contact. This thin electrolyte can be coated directly on the photoconductor and pressed thereto by a metallic anode. If the electrolyte contains silver ions (and preferably some thiourea for intensification), the metallic electrode can be of any metal. Alternatively the electrolyte can be made ionic by any suitable salt such as potassium nitrate and a silver anode may be used to provide the silver ion when the current starts to flow through the electrolyte. Other metal anodes give useful but inferior results in the latter case.

In the embodiments of the invention which use silver halide as a solid electrolyte, with a contacting layer of metal or Water coated extremely thin on the photocon ductor, the silver halide may be provided on the surface of a silver roller. The roller acts as an anode as it is rolled in contact with the exposed zinc oxide in resin (thinly overcoated) layer. The silver bromide electrolyte provides the silver ions which are plated onto the photoconductor as an image and these silver ions are replenished in the silver halide coating from the silver roller itself. The roller may carry sufiicient moisture for contact without wetting the photoconductor.

As pointed out above the electrically conducting material between the silver halide and the photoconductor must be less than 0.0003 cm. thick and have an optical transmission density of less than 0.3. Its minimum is defined by the fact that it must be thick enough to be in effectively uniform electrical contact with both layers. In the case of water, it fills the minute roughness structure of the photoconductor surface. In the case of metal it may not fill such structure to level since the metal on the high points contacts the silver halide and is in turn in contact with both the high points of the photoconductor surface and laterally with the metal extending into the low points. The structure is so fine that resolution is not afiected and the electrical contact is thus effectively uniform. This effective uniformity holds for the water too in spite of minute differences in thickness of the water layer in the structure of the photoconductor surface.

Absolutely dry gelatin would A Other objects and advantages of the invention will be apparent from the following description when read in connection with the accompanying drawing in which:

FIG. 1 schematically illustrates the operation of the invention.

FIGS. 2 to S similarly illustrate in enlarged cross section various forms of the electrolytic units which may be used in the process illustrated in FIG. 1.

FIG. 6 schematically illustrates a preferred embodiment of the invention.

In FIG. 1 a photoconductive layer 10 consisting of photoconductive zinc oxide in resin is coated on an alu'= minum foil 11 laminated to a paper support 12. The zinc oxide in resin has been exposed and contains a conductivity image. Current is passed from a source of potential indicated schematically at 15 through an electrode 16 and an electrolyte 17 to the zinc oxide photoconductor 10 which acts as a cathode in this case. The non-uniform surface 18 of the zinc oxide in resin is shown by the exaggerated waviness of this surface as seen in cross section. Actually more than physical unevenness is involved. There must be intimate contact with the zinc oxide itself. This is not easy to accomplish; probably some surface phenomenon is involved. The electric contact between the electrolyte l7 and the zinc oxide in resin layer 10 must be intimate even though the electrolyte 17 is a dry one. Normally available pressures are not sufficient to provide this intimate contact if the electrolyte is silver bromide for example. Hence a contacting layer is used in such cases. On the other hand reasonable pressure is sufficicnt to provide the contact if the electrolyte is dry (apparently dry) gelatin.

FIG. 2 illustrates one embodiment of the invention which provides the necessary intimate electrical contact between a silver halide crystalline layer and a Zinc oxide in resin layer. In FIG. 2 the anode is a silver plate 21 whose surface has been treated to provide a silver halide layer 22 thereon. Aluminum or silver metal is coated, for example by vacuum evaporation, or by chemical means, onto the surface of the Zinc oxide to form a thin metal layer 23. The layer is so thin as to be practically invisible to the unaided eye. It has no appreciable density. The zinc oxide is exposed through the metal layer before the metal layer 23 is brought into contact with the silver halide 22. Pressure is applied as shown symbolically by rollers 25 and 26. This has been found to give adequate and intimate electrical contact with the Zinc oxide and to produce a high resolution, high density, silver image on the surface of the metal 23 and zinc oxide layer 10. The present invention finds its greatest use with zinc oxide photoconductors.

FIG. 3 illustrates an alternative embodiment in which the exposed zinc oxide layer 10 without any metallic overcoating is pressed into contact with the silver halide layer 22 but a single tiny drop of water is placed between the two layers as they are brought into contact and spreads over the whole surface of the Zinc oxide due to the high pressure applied. Alternatively, the zinc oxide could be wetted, but this would eliminate the advantages due to the dryness of the system. It is noted that the electrolye itself, namely silver halide is dry and that the water is merely to provide the intimate electric contact in the same way as the metal in FIG. 2. This is not a wet electrolyte process. When the zinc oxide layer with the image plated thereon is separated from the silver halide, it is substantially dry and no moisture is detected.

In FIG. 4 a very thin layer of gelatin is coated directly on the zinc oxide in resin layer and allowed to dry completely. The gelatin contains a small percentage of glycerol as given in the examples below and a small per-. centage of potassium nitrate so as to be ionic. Even after several days of drying in contact with normal atmospheric humidity the gelatin contains suflicient moisture to be electrically conducting, but not suflicient to be moist or 75 to appear moist in any way. Since metal, preferably silver, ions are required in the process illustrated in FIG. 4 the anode 31 is metal (preferably silver) in this case and the current passes through the gelatin electrolyte between the metal anode and the zinc oxide cathode, depositing silver as an image on the zinc oxide in resin layer. The gelatin layer is so thin that the location in section of the silver is not apparent to the unaided eye but the silver image appears on the gelatin and zinc oxide layer when the anode 31 is removed. It is believed to be on the interface between the gelatin and the photoconductor.

In FIG. 5 the thin substantially dry gelatin layer 35 contains silver nitrate which supplies the silver ion and thiourea which intensifies the silver image when deposited, presumably by the formation of silver sulfide. The gelatin also contains glycerol as a humectant. The electrode 36 may be of any metal since the silver ions are already in the electrolyte. The silver deposits at the surface of the zinc oxide layer and removal of the gelatin after the image is so formed, removes the residual silver nitrate so as to prevent staining and darkening of the print. The arrangement shown in FIG. 4 does not require any such fixing operation.

FIG. 6 illustrates a continuous operation using the principle illustrated in FIG. 2 (or FIG. 3). A photoconductive layer 40 of zinc oxide in resin is coated on a conducting base 41 and overcoated with an extremely thin layer of metal 42. The photoconductor is exposed through the metal layer 42 by a scanning operation. A lamp 45 illuminates a transparency 46, the image of which is focused by a lens 47 on the photoconductive layer 40. The transparency moves to the left as indicated by the arrow 48 and the photoconductive layer 40 moves synchronously with the .image of the transparency as indicated by the arrow 49. Immediately following exposure, the photoconductor is passed between pressure rollers 51 and 52. The roller 51 consists essentially of silver with a silver halide coating 53 on the surface thereof. Potential is applied by a DC. source indicated schematically at 54. The current passes through the exposed area of the photoconductor 40 and through the dry electrolyte 53 to deposite silver, imagewise distributed, on the surface of the metal 42 and photoconductor 40. The material 42 is so thin as not to be noticeable.

Using the principle of FIG. 3, the metallic layer 42 may be omitted and the surface of the silver halide 53 may be moistened by a moistening roller similar to those used in lithographic printing. The quantity of moisture must be sufficient to provide intimate electrical contact between the silver halide and the photoconductor 40, but not sufficient to noticeably dampen the photoconductor.

Example 1 A thin layer of aluminum was evaporated by vacuum distillation onto the surface of a zinc oxide in styrene butadiene resin coated on an aluminum foil paper laminate. A sheet of silver was iodized by exposure to iodine vapor for 20 minutes, so that the surface thereof constituted silver iodide. This plate and the aluminum coated Zinc oxide, after exposure of the Zinc oxide in contact with line copy negative to an illumination of 400 ft. candle seconds were pressed into contact and 80 volts D.C. was applied between the aluminum foil on which the zinc oxide was coated and the sheet of silver, for 5 seconds. In the preferred case the BC. was applied so that the Zinc oxide layer was cathode and the image deposited thereon. High definition, good density prints were obtained on the zinc oxide layer. In another case the DC. current was applied with the opposite polarity and the image deposited on the silver iodide.

Example 2 This example is the same as Example 1 except that the surface of the silver plate was bromided by exposure to bromine vapor for 20 minutes to form silver bromide as the solid electrolyte. Again good quality prints were obtained in the zinc oxide layer.

6 Example 3 Stoichiometric quantities of silver iodide and mercuric iodide were heated to form the complex salt of silver mercuric iodide. This was pressed out to a thin layer on electrically conducting glass sold under the trade name Nesa. The complex halide, when heated above 50 0., had increased ionic conductivity and acted as an excellent solid electrolyte in contact with the aluminum coated zinc oxide for the electrolytic formation of high quality images on the zinc oxide and aluminum.

Examples 4, 5 and 6 are identical to Examples 1, 2 and 3 respectively except that silver was evaporated onto the zinc oxide layer rather than aluminum. Again high quality prints were obtained. The evaporated silver coat ing merely acts as a contacting layer and is extremely thin.

Examples 7 and 8 These examples were similar to Examples 1 and 2 except that no metal was evaporated onto the zinc oxide resin photoconductor. Instead, a single drop of water was placed between the silver iodide (Example 7) or silver bromide (Example 8) and the zinc oxide layer. Five pounds pressure per square inch was applied to spread this moisture over the entire area. These examples were repeated using as the small drop of moisture several different electrolytes and in one case just distilled water. Very little difference was noted for the various electrolytes and the distilled water. This appears to indicate that the presence of a small amount of water is sufficient to provide intimate electrical contact between the two layers and that there is no need for electrolytic action in this contacting layer itself. Silver mercuric iodide could be used in place of silver iodide or silver bromide of these Examples 7 and 8. The term silver halide is used in this specification to include the complex halides such as silver mercuric iodide.

Example 9 A solution was made containing /2 g. potassium nitrate, 2 g. gelatin and 7 drops of glycerol in 200 cc. distilled water. This solution was coated with a spray gun on dye sensitized zinc oxide photoconductographic material, coated on a metal foil laminate and the coating was dried for 3 days. At the end of this time there was no indication of moisture; the coating was not sensibly wet or tacky.

The coated recording material was exposed to an image of 400 ft. candle seconds and was immediately placed down on a previously cleaned silver plate. Contact between the recording material and the silver plate was achieved by pressure. The pressure does not have to be excessively large since the gelatin conforms to the surface in contact. A potential of 30 volts was applied for 10 seconds between the silver plate and the aluminum backing of the recording material, the silver plate being positive. A well defined image of good Dmax was found on the recording material [after separation from the silver plate. This example was repeated several times using different materials in place of silver as the anode. For example brass, copper and aluminum all produced legible images but the quality appeared to 'be somewhat inferior to that produced by the silver plate. Again, conducting Nesa glass and conducting rubber rollers were tried as the anode and were successful but not quite as good as the silver plate.

Example 10 This is similar to Example 9 except that the solution sprayed on the zinc oxide contained 2 g. silver nit-rate, 8 g. thiourea, 2 g. gelatin, 30 drops of glycerol, and 15 drops of a solution of wetting agent in 200 cc. distilled water.

Having thus described various embodiments of our in vention, we wish to point out that it is not limited thereto but is of the scope of the appended claims.

We claim:

1. A dry photocon-ductographic process comprising passing a D.C. current through a dry photoconductive layer containing an imagewise distribution of conductivity variations as cathode and through 13. dry electrolyte layer comprising a water permeable solid vehicle containing silver ions and a small percentage of compatible humectant sufficient to provide flexibility and conductivity but insufficient to create moistness when the dry electrolyte layer is exposed to atmospheric humidities up to 85% relative humidity, which dry electrolyte layer is in intimate electric contact with the dry surface of the photoconductive layer and is pressed thereto by a dry metal anode.

2. A dry photoconductographic process comprising passing :a DC current through a dry photoconductive layer containing an imagewise distribution of conductivity variations as cathode and through a dry electrolyte layer comprising a water permeable solid vehicle containing, before the current starts to pass, non-metallic ions and a small percentage of compatible humectant sufiicient to provide flexibility but insufficient to create moistness when this dry electrolyte layer is exposed to atmospheric humidities up to 85% relative humidity, which dry electrolyte layer is in contact with the dry surface of the photoconductor and is pressed thereto by a dry silver anode from which silver ions enter the electrolyte when current passes and deposit as metallic silver on the surface of the photoconductive layer.

3. A dry photoconductographic process comprising passing a DC, current through :a dry photoconductive layer containing an imagewise distribution of conductivity variations and through a dry layer consisting exclusively of a dry solid mass of silver halide pressed onto the dry photoconductive layer with an electrically conducting material less than 0.0003 cm. thick and having an optical density in transmission of less than 0.3 between the halide and the dry photoconductor, and thick enough to be in effectively uniform electrical contact with both the halide and the photoconductor.

4. The process according to claim 3 in which the solid silver halide layer is on the surface of a metal roller, rolling on the photoconductive layer.

5. A dry photoconductographic process comprising passing a DC. current through a photoconductive layer containing an imagewise distribution of conductivity variations and through a dry layer of silver halide pressed onto the photoconductive layer with a substantially invisible layer of electrically conducting metal less than 0.0003 cm, thick and having an optical density in transmission of less than 0.3 between the halide and the photoconductor, and thick enough to be in efi'fectively uniform electrical contact with both the halide and the photoconductor, said silver halide being on the surface of a metal roller, rolling on the photoconductive layer.

6. A dry photoconductographic process comprising passing a DC. current through a photoconductive layer containing an imagewise distribution of conductivity variations and through a dry layer of silver halide pressed onto the photoconductive layer with a substantially invisible layer of electrically conducting metal less than 0.0003 cm. thick and having an optical density in transmission of less than 0.3 between the halide and the photoconductor, and thick enough to be in effectively uniform electrical contact with both the halide and the photoconductor.

7. The process according to claim 3 in which the electrically conducting material is essentially water present in such small quantities as not to moisten the surfaces but sufiicient to provide intimate electrical contact between the photoconductor and the solid mass of silver halide,

8. The process according to claim 3 in which the solid silver halide layer is on the surface of a metal roller, rolling on the photoconductive layer and the electrically conducting material is water applied to the surface of the silver halide roller in sufiicient quantity to provide intimate electrical contact with the photoconductor but not sufiicient to moisten the photoconductor.

References Cited by the Examiner UNITED STATES PATENTS 2,692,178 10/1954 Grandadam 96-1 2,764,693 9/1956 Jacobs et al. 96-1 2,866,903 12/1958 Berchtold 96-1 3,010,883 11/1961 Johnson et a1 204-18 3,010,884 11/1961 Johnson ct a1 204-18 FOREIGN PATENTS 155,623 2/1939 Austria.

151,971 5/1904 Germany.

464,112 4/1937 Great Britain.

OTHER REFERENCES Varden: Modern Photo, January 1958, pp. 34 and 38.

WINSTON A. DOUGLAS, Primary Examiner,

PHILIP E. MANGAN, JOSEPH, REBOLD,

JOHN H. MACK, Examiners. 

1. A DRY PHOTOCONDUCTOGRAPHIC PROCESS COMPRISING PASSING A D.C. CURRENT THROUGH A DRY PHOTOCONDUCTIVE LAYER CONTAINING AN IMAGEWISE DISTRIBUTION OF CONDUCTIVITY VARIATIONS AS CATHODE AND THROUGH A DRY ELECTROLYTE LAYER COMPRISING A WATER PERMEABLE SOLIDE VEHICLE CONTAINING SILVER IONS AND A SMALL PERCENTAGE OF COMPATIBLE HUMECTANT SUFFICIENT TO PROVIDE FLEXIBILITY AND CONDUCTIVITY BUT INSUFFICIENT TO CREATE MOISTNESS WHEN THE DRY ELECTROLYTE LAYER IS EXPOSED TO ATMOSPHERIC HUMIDITIES UP TO 85% RELATIVE HUMIDITY, WHICH DRY ELECTROLYTE LAYER IS IN INTIMATE ELECTRIC CONTACT WITH THE DRY SURFACE OF THE PHOTOCONDUCTIVE LAYER AND IS PRESSED THERETO BY A DRY METAL ANODE. 